The present invention relates to a matrix type fuel cell using an electrolyte such as phosphoric acid and, more particularly, to a structure for a fuel cell in which a number of cell elements are stacked through ribbed separate plates called bipolar plates and each formed in both its upper and lower faces with grooves defining reactive gas supply passages for supplying reactive gases such as fuel gases and air to the anode and cathode of the corresponding one of the cell elements.
First of all, the structure of the above-specified fuel cell according to the prior art will be explained with reference to FIG. 1. Indicated at reference numeral 1 in FIG. 1 is a cell element which is constructed by sandwiching between an anode and a cathode a matrix layer impregnated with an electrolyte. The cell elements 1 and separate plates indicated at numeral 2 are alternately stacked to construct a fuel cell stack. Here, each of the separate plates 2 is made of a gas-impermeable carbon plate and is formed in its upper and lower faces with numerous grooves of two groups which extend at a right angle to define reactive gas supply passages 3 and 4 for supplying fuel gases and air, respectively. In the fuel cell thus constructed, the fuel gases and the air are supplied in the directions of arrows from the outside through not-shown manifolds to the reactive gas supply passages 3 and 4 of the separate plates 2, from which the reactive gases are further supplied to the respective electrodes of the sandwiched cell element 1 so that a galvanic reaction is caused to produce electricity, as is well known in the art.
Incidentally, in order to have an efficient run of the fuel cell using the aforementioned phosphoric acid as an electrolyte, the fuel cell is run while having its temperature maintained usually at about 190.degree. C. While a heat of reaction corresponding to the energy of the produced electricity is generated by the galvanic reaction, the fuel cell has to be cooled so that it may be maintained at the above-specified running temperature. In the cooling method of this case, generally speaking, water, gases, oil and so on are used as a coolant. One of the most generally adopted method is conducted by supplying the air at a higher flow rate than that required for the galvanic reaction to the air supply passage of the separate plates 1 and by allowing the air to be partially consumed by the galvanic reaction while carrying the generated heat of the cell by the flow of the excess air.
Generally, the electrolyte such as the phosphoric acid held in the matrix layer of the cell element evaporates and scatters out and is carried to the outside of the cell by the flow of the reactive gases so that the content in the matrix layer is gradually decreased. The loss of the electrolyte in this case increases in proportion to the flow rate of the reactive gases. As a result, the method of cooling the fuel cell by excessively supplying the air or the reactive gas, as has been described above, cause a high rate of the electrolyte to be scattered and lost. Thus, the fuel cell is hard to run efficiently and safely for a long time. This makes necessary the troublesome running operation such as frequent supplies of the electrolyte in the course of the run. The method of using water as the cooling medium has a complicated structure of a cooling system including a water piping line because it is necessary to prevent the cell from being short-circuited by the cooling medium and the water piping line from interfering with the manifolds of the reactive gas supply systems.
According to one method, there has been adopted a structure in which a cooling plate is arranged for every several cell elements and cooling water pipes are piped through the cooling plate. In this method, the cooling effect is high for the cell elements adjacent to the cooling plates but is low for the remaining cell elements spaced from the cooling plates. This establishes a difference in the temperature distribution between the cell elements constructing the cell stack, so that a proper cell cooling effect cannot be achieved.
There is also known a method in which air is used in place of the water as the cooling medium and in which cooling air passages are opened in cooling plates fitted for every several cell elements in the cell stack of the fuel cell for supplying the air through common manifolds together with the aforementioned reactive gas or air so that a portion of the air is supplied as the reactive gas to the electrodes of the cell elements whereas the remaining portion is guided to flow through the air passages of the cooling plates to strengthen the cooling effect of the cell, as is disclosed in Japanese Patent Laid-Open No. 154181/1983. However, this method is also accompanied like the aforementioned cooling water method by the temperature distribution difference between the cell elements constructing the cell stack. Since the reactive gas supply passages and the cooling air passages are opened in the common manifolds, it is difficult to dispense and adjust the air flow rates inbetween. If the flow rate of the air to be introduced into the manifolds is increased so as to increase the draft of the cooling air, the air supply rate to the reactive gas supply passage is necessarily increased at the same time. This creates an excess supply of air, which is more than that required for the galvanic reaction. Hence, the scatter and loss of the electrolyte is increased.